This invention relates to a hydrostatic steering system, particularly for a motor vehicle of a type having a spring centered control element actuated by the vehicle's steering wheel for operation of a fluid servomotor in accordance with its rotational direction and rotational speed.
In hydrostatic steering systems of the foregoing type, there is no mechanical connection between the steering wheel and the vehicle wheels being steered. Generally, such hydrostatic steering systems are feasible only for slow running vehicles such as tractors, combines, loading fork stackers and the like wherein vehicle speed is limited to 50 kph. Such a steering system is disclosed, for example, in German Pat. No. 2633011, consisting of a steering control member centered by a rotational rod and in the form of axially slideable element for control of at least one servomotor by the supply and exhaust of fluid pressure generated by a manually operable pump as well as a high pressure pump driven by the vehicle engine. The fluid flow path from the high pressure pump is directed in accordance with the rotational direction imparted to the steering wheel and its rotational speed through the steering control member and the manual pump to the servomotor. The fabrication of the steering control member is very expensive because of a plurality of steering control grooves and bores therein as well as the formation of gear teeth thereon. The manual pump formed as a rotary type pump with a control disc and a propelling drive shaft, is also considerably costly because of surface finishing of its parts. Furthermore, such a steering system operates with a relatively high power loss because the high pressure pump usually delivers pressurized fluid at an unnecessarily high rate of flow with the entire pressurize fluid being returned to the reservoir tank even in the neutral position of the steering control system through the steering control member.
It is therefore an object of the present invention to provide a hydrostatic steering system of relatively simply construction and capable of being fabricated at a reasonable cost with a capability of generating high steering forces in response to relatively low energy input. A further object is to provide a steering control system capable of meeting present day requirements in the utilization of the high pressure pump associated therewith by virtue of its functional interrelationship with the operating pressurized fluid system.